This is WEEKEND EDITION from NPR News. I'm Wade Goodwyn. Rachel Martin is away. Syrians and the world have spent the last week bracing for a U.S. attack on Damascus that seemed to be imminent. Now, President Obama has surprised everyone by pushing the pause button and by announcing yesterday in the Rose Garden that he will go to Congress for approval. NPR's Ari Shapiro reports from the White House.

ARI SHAPIRO, BYLINE: Day by day, President Obama and his aides have been building the case for a strike on Syria. American warships moved closer to the Syrian coast as the president moved closer to a decision. Yesterday afternoon, Obama definitively announced he has made up his mind.

PRESIDENT BARACK OBAMA: I'm confident that we can hold the Assad regime accountable for their use of chemical weapons, deter this kind of behavior and degrade their capacity to carry it out.

SHAPIRO: That was hardly a surprise. But what came next was a dramatic twist.

OBAMA: I've long believed that our power is rooted not just in our military might, but in our example is a government of the people, by the people and for the people. And that's why I've made a second decision. I will seek authorization for the use of force from the American people's representatives in Congress.

SHAPIRO: It's a political gamble for the president. Not one week ago in London, the House of Commons shot down British Prime Minister David Cameron's bid for similar approval. For Cameron, it was a humiliating defeat. White House aides say they're confident Obama can avoid that fate. The president used his Rose Garden speech to lay out parts of the case.

OBAMA: Here's my question for every member of Congress and every member of the global community: What message will we send if a dictator can gas hundreds of children to death in plain sight and pay no price?

SHAPIRO: Senior administration officials say this idea took shape less than 24 hours before the president made the announcement. And they say it came from Obama alone. The entire administration had been on the march towards a strike. Then, on Friday, the President had his daily wrap-up meeting with White House chief of staff Denis McDonough. They walked laps around the South Lawn of the White House. And the president told McDonough if Congress wants to be consulted, they should do more than consult. They should have to go on the record for or against military action. After 45 minutes, the walk ended and Obama called his national security team into the Oval Office. The speech took shape late Friday night. And on Saturday, Obama informed Congress of his plans before heading into the Rose Garden.

OBAMA: So, this morning I spoke with all four Congressional leaders, and they agreed to schedule a debate and a vote as soon as Congress comes back into session.

SHAPIRO: Congress does not return from vacation until September 9th. And so, President Obama says, he relied on this important assurance from military leaders.

OBAMA: Our capacity to execute this mission is not time-sensitive. It will be effective tomorrow, or next week or one month from now.

SHAPIRO: As he spoke, you could hear faint chants in the background. About 100 protesters marched in front of the White House with signs that said: Hands off Syria, and Bombing Syria doesn't protect people, it kills people.

CROWD: (Chanting) Hands off Syria. Obama, hands off Syria, Obama.

SHAPIRO: Retiree Debbie Hamrahand does not believe President Obama's assurances that this will be a short intervention.

DEBBIE HAMRAHAND: Why would we want to go into this very chaotic situation? We don't know who's who and what's what, and by just lobbing a few cruise missiles into something doesn't mean that could even be the end of it. It's the start of something.

SHAPIRO: In the Rose Garden, Obama said he appreciates that people are tired of war. That's one reason he wants the blessing of the people's representatives in Congress.

OBAMA: We all know there are no easy options. But I wasn't elected to avoid hard decisions, and neither were the members of the House and the Senate.

SHAPIRO: The president also plans to make the case internationally. This week he leaves for the G20 summit, where he'll lobby America's allies abroad to climb aboard. Ari Shapiro, NPR News, the White House. Transcript provided by NPR, Copyright NPR.